postgres安装完成后使用psql命令进入控制台（默认无需密码）
使用\password命令，为postgres用户设置一个密码

\password postgres

创建数据库用户rails_payment，并设置密码。
CREATE USER rails_payment WITH PASSWORD 'rails_payment';

ActiveRecord::StatementInvalid: PG::InsufficientPrivilege: ERROR: permission denied to create database

Lisas-Mac-2:~ postgres$ psql
psql (9.6.1)
Type "help" for help.

postgres=# \password postgres
Enter new password:
Enter it again:
postgres=# CREATE USER rails_payment WITH PASSWORD 'rails_payment';
CREATE ROLE
postgres=# CREATE DATABASE payment_dev OWNER rails_payment;
CREATE DATABASE
postgres=# CREATE DATABASE payment_test OWNER rails_payment;
CREATE DATABASE
postgres=# CREATE DATABASE payment_pro OWNER rails_payment;
CREATE DATABASE